The field of the invention is centrifugal processors used in manufacturing flat media products.
The production of semiconductor wafers, substrates and photomask plates used in the manufacture of semiconductor wafers, has typically utilized processing equipment in which various types of processing fluids are used to treat the wafers. One example of a semiconductor processor is a centrifugal rinser-dryer used to rinse acids, caustics, etchants and other processing fluids from wafers, photomask plates, and similar units. The rinser-dryers are also used to dry the rinsed units using a flow of heated gas, such as nitrogen which is passed through the processing chamber after rinsing with the desired fluid. The wafers are spun during processing to provide more even distribution of the processing fluids across the wafer surfaces, and to assist in removal of rinsing liquids in preparation for drying.
Other types of semiconductor processors include acid and caustic treatment machines which spray or otherwise apply acids and caustics to the wafers or other flat media. Stripping processors are used to remove photoresist from the wafers. Other specific processing of semiconductors may require other types of chemicals. Many of these processes are appropriately performed in centrifugal processing machines to provide for even distribution of fluids over the wafer and to aid in removal of liquids.
A primary problem in the production of semiconductors is particle contamination. Contaminant particles can affect the photographic processes used to transfer the chip layouts onto the wafers being processed into chips. Contaminants on the photomasks can cause deterioration of the image being transferred onto the wafer. The direct processing of the wafers or other flat media themselves is even more susceptible to contamination because of the numerous processing steps, and the risk at each stage that contaminating particles can become adhered to the surface of the wafer. Particle contamination typically causes a large number of the chips in a wafer to be defective. Thus it is very important to reduce contamination to increase yields.
With higher resolution now made possible through newer semiconductor processing techniques, the effects of contaminants has become even more of a problem than in the past. In the past, contaminant particles smaller than 1 micron did not cause defects as minimum feature sizes were 2 microns or larger. However, now the feature size used in high density chip designs is substantially smaller, e.g., 0.18 micron. Planning is already progressing for even higher density chips which require even smaller feature sizes. The move toward smaller feature sizes is compounding the contamination problem because of the greater difficulty in controlling smaller particles and the greater numbers of smaller particles in the processing environment. If contaminants are present, then substantial numbers of the resulting chips can be rendered defective and unusable, at substantial cost to the manufacturer.
The causes of contaminating particles on wafer surfaces occurs from numerous sources. Each of the processing chemicals used is necessarily impure to some small degree. The water used in processing is deionized to remove metallic ions and other impurities, but such supplies also contain some impurities. Environmental dust carried in the air in which the wafer is moved between the various processing machines also causes contamination. To reduce this environmental contamination, manufacturers of semiconductors have built production areas which have relatively low amounts of environmental dust. These so-called "clean rooms" are extremely expensive to build and expensive to operate in a manner which maintains contaminant particle levels at acceptable low levels. With the decrease in feature size to provide more dense chips, the difficulties in providing sufficiently low environmental dust levels have increased.
Contamination near the center of the wafers has been a long standing problem associated with centrifugal processing machines. The centrifugal forces acting on the fluid droplets on a wafer are directly proportional to the distance between the fluid droplet and the spin axis of the wafer. Consequently, the centrifugal force acting on fluid droplets at or near the spin axis may be insufficient to fling the droplets off of the wafers. As a result, semiconductor chips which are subsequently formed on the wafers at or near the spin axis, will often be defective, because of impurities left there by "spotting", i.e., removal of a fluid droplet by evaporation, rather than by centrifugal force.
Centrifugal processors are installed in clean rooms, along with other semiconductor processing equipment, to minimize contamination of the wafers. Due to the cost and complexities of clean room installations and operations, the centrifugal processors are necessarily compact. The wafers, which are e.g., 200 mm in diameter, are spaced apart by only a few millimeters within the centrifugal processor. As a result, there is little air or gas flow across the centers of the wafers. Some existing centrifugal processors spray dry nitrogen across the wafers. See, for example, U.S. Pat. Nos. 5,022,419 and 4,300,581, incorporated herein by reference. While spraying dry nitrogen across the wafers, to remove droplets at or near the wafer centers, is effective, it consumes large amounts of nitrogen, at a significant cost. Accordingly, difficulties remain in achieving cost effective high production yields in manufacturing semiconductors and other flat media. It is therefore an object of the invention to provide an improved centrifugal processor for processing flat media, such as silicon wafers.